Electrolyte : 0.1M NaOH, V= 230mL, Oxygen purging was done for 30 mins before starting the experiment and was purged for 10 mins between the experiment. Up to 900 rpm I can see increase in current with rpm but for 1200, 1600 n 2500 rpm current almost stays constant. I feel its because electrolyte is not saturated enough with oxygen.
Increase in flux of oxygen on electrode surface at higher rpm should give more current at higher rpm but I am observing saturation after 900 rpm. Any suggestions?
Usually I do ORR in two step, first step involves complete purging of the solution with argon for 30 minutes and and then I record a CV in argon . After that I purge the solution in oxygen for an hour, I do ORR. I never saw what u observed. May be u can give a try. You are right because of increase in flux of oxygen on electrode surface, one should observe higher current at higher RPM.
I am also using 5mm GC electrode and before performing my experiment i thought of doing a control experiment with GC electrode. Which n how much of electrolyte do you use ( I use 230 mL 0.1M NaOH). I have never done argon purging i will try it
i usually use approx. 50 ml. because the capacity of the cell (I use) is around 100 ml.
I am also using ~100mL cell with 5mm GC electrode from Pine Instruments, I would say after Ar-gas purging first (as Aditi said), then purge oxygen for 1 hour and keep the oxygen flow on the surface of electrolyte to cover the surface with oxygen bubbles while doing RDE-polarization curves. It would improve the currents at higher RPM
If this all does not work, you should check, if the area of your counter is high enough. Sometimes, it is a limiting factor. I perform ORR after bubbling the electrolyte for 15 min. During the LSV the solution is overflown with the O2 gas. My counter is made of arolled Pt mash 5x5 cm, which is connected with a Pt wire. The surface area of a wire was not sufficient for measurements with 1600 rpm.
I am also doing ORR with GC I never face such problems.. I purge O2 during the ORR also ..(upper part of the solution) .. you may try few more times.. I have a question.. Pls anybody answer.. GC electrode is not giving ORR response in Acidic (H2SO4 solution).. So far, I know that strong adsorption of anions on GC surface which hindered the ORR on GC in acidic solutions.. Is there any other reasons, Why GC is not active in acidic solution towards ORR..
If you use 0.1M HClO4 instead, you can get rid of the problem of of strong adsorption of anions on to GC electrode. But I do not know any other reasons why ORR do not work in H2SO4.
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